Polyester yarn

ABSTRACT

Improved multifilament polyester yarn has good processibility on knitting machines and provides good fabric bulk when used in combination with ordinary polyester yarn. The yarn is an assembly of low-shrinkage, continuous filaments of synthetic linear condensation polyester which are substantially free of crimp. The filaments are drawn and relaxed under conditions which provide a yarn having a sonic velocity value of 1.9 to 3.0 kilometers per second, an X-ray crystallinity value of 16 to 35 percent, and a single shrinkage-tension peak at a temperature below 100*C.

United States Patent [191 Pacoisky July 31, 1973 POLYESTER YARN [75] Inventor: Edward Anthony Pacofsky, Kinston,

[73] Assignee: E. 1. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Aug. 4, 1971 [21] Appl. No.: 168,953

[52] US. Cl. 57/140 R, 57/157 R, 264/290 R [51] Int. Cl D03g 3/02 [58] Field of Search 57/34 B, 157 F, 157 S,

57/140 R, 140 BY, 157 R; 28/104, 72.12, 72.17; 264/290 R, 290 N, 210 F [56] References Cited UNlTED STATES PATENTS 3,662,440 5/1972 Hill et al. 28/72.l7 3,069,836 12/1962 Dahlstrom et al 57/157 F 3,199,281 8/1965 Maerov et al. 57/140 BY 3,261,071 7/1966 Clendening et a1 28/l.4

3,303,169 2/1967 Pitzl 57/157 F 3,421,194 l/1969 Breen et al. 28/72.!2 3,423,809 l/l969 Schmitt 57/157 F 3,452,130 6/1969 Pitzl 264/290 N 3,452,131 6/1969 Geerdes et al. 264/290 R Primary Examiner-John Petrakes Attorney-Norris E. Ruckman [57] ABSTRACT 5 Claims, 2 Drawing Figures PATENIEU Jul 3 1 3. 748 844 INVENTOR EDWARD ANTHONY PACQFSKY Mi-M ATTORNEY POLYESTER YARN BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel textile yam. More specifically, it is concerned with a new synthetic polyester textile yarn particularly suited for the manufacture of improved knitwear.

2. Description of the Prior Arts Synthetic polyester fibers, such as those described by Whinfield & Dickson in U.S. Pat. No. 2,465,319, have become important articles of commerce. Early fabrics prepared from melt spun polyesters were characterized by a slick handle and by lack of bulk, and many methods to improve the tactile aesthetics and bulk of polyester fabrics have been developed. These include many mechanical crimping treatments, such as the one described by Arnold in U.S. Pat. No. 3,335,477, which are usually followed by cutting the crimped filaments into staple fibers that are processed into yarn in a manner similar to that used for natural fibers. Many procedures have also been proposed for the improvement of continuous filament yarn. For example, Breen U.S. Pat. Nos. 2,783,609 and 2,852,906 describe a textured yarn which is characterized by filament convolutions and which provides fabrics with improved bulk and tactile aesthetics. Steam or hot air can be used in a jet bulking apparatus to provide, under proper conditions, a stable crimped yarn which does not require twist to hold the filament convolutions in place. A yarn with a highly desirable stable crimp having a random, threedimensional, curvilinear, extensible configuration is described by Breen et al. in U.S. Pat. No. 3,186,155 and an improved process for preparing such yarns is described by Scott in U.S. Pat. No. 3,143,784. Bulk has also been obtained by using yarns which are composed of filaments exhibiting differential shrinkage characteristics, as described by Maerov & McCord in U.S. Pat. No. 3,199,281 and by Waltz in U.S. Pat. No. 2,979,883. Such yarns are postbulkable in the sense that a non-bulked yarn may be woven into fabric and then bulked later by a heat treatment which activates the differential shrinkage characteristics. Another method of producing a post-bulkable yarn of this general type is described by Jamieson & Reese in U.S. Pat. No. 2,980,492, where the differential shrinkage characteristic is obtained by combining filaments of different denier. More recently, U.S. Pat. No. 3,454,460 to Bosely has described a highly desirable postbulkable yarn composed of bicomponent filaments capable of developing a helical crimp. Other methods of improving bulk and handle of polyester fabrics have included the use of a novel spontaneously elongatable polyester filament, as described by Kitson & Reese in U.S. Pat. No. 2,952,879, which may be combined with ordinary polyester filaments to obtain differential shrinkability.

Although desirable results have been achieved in improving the bulk and tactile aesthetics of fabrics of continuous filament polyester yarn by prior methods, further improvements are needed in specific end uses, such as knitwear, where pre-bulked continuous filament yarns give poor processibility and known postbulkable yarns are either excessively costly to prepare or do not provide the properties desired.

One method of improving warp knit fabrics, described by Kasey in U.S. Pat. No. 3,041,861, utilizes a low shrinkage yarn fed to the top (front) bar of a knitting machine in combination with a high shrinkage yarn fed to the bottom (back) bar of the machine. Subsequent heating of the fabric causes the two yarns to shrink different amounts, which results in improved fabric covering power. Bulk, however, is not significantly improved.

SUMMARY OF THE INVENTION The present invention provides a novel continuous multifilament polyester yarn eminently suitable for use in the preparation of improved apparel, particularly knitwear. The yarn provided is prepared by an economical process, exhibits good processibility on knitting machines, and is capable of giving fabrics having excellent bulk and handle when used in combination with ordinary commercially available polyester yarns. The excellent processibility in knitting is in large measure due to the fact that the yarns are essentially crimpfree, and develop little or no crimp upon heating. In view of this lack of significant crimp, it is quite surprising that excellent bulk and tactile aesthetics are developed when fabrics containing these yarns are heated.

The improved multifilament yarn of the present invention is an assembly of low-shrinkage, continuous filaments which are substantially free of crimp. The yarn consists of synthetic linear condensation polyester and is characterized by having an orientation, as measured by sonic velocity, of 1.9 to 3.0 kilometers per second, an X-ray crystallinity value of 16 to 35 percent, and a single shrinkage-tension peak at a temperature lower than 100C. The preferred yarns of the invention have a boil-off shrinkage of 1 to 10 percent and a sonic velocity value between 2.0 and 2.5 kilometers per second. The shrinkage-tension peak is determined for temperatures between 60 and 200C. Preferably, this peak is at a temperature between and 100C. and the peak tension is less than about 0.06 gram per denier. Particularly good fabric bulk is obtained with yarns consisting essentially of ethylene terephthalate polyester, which may be modified slightly as illustrated in Example II for basic dyeability.

The novel yarn of the invention is prepared by a simple, low-cost manufacturing process characterized by a critical combination of spinning, drawing, and relaxing conditions not previously disclosed for polyester yarns. The process comprises melt-spinning a synthetic linear terephthalate polyester into filaments; quenching the filaments and combining them into a multifilament strand; drawing the multifilament strand at a temperature above C. between feed rolls and draw rolls; heating the drawn strand in a substantially tensionless state in a plasticizing medium to cause it to shrink in the longitudinal direction; and then cooling and winding the strand. The process is characterized by the use of a low draw ratio within the range of about 2:1 to 3:1 to provide a drawn multifilament strand having a sonic velocity value within the range of 1.9-3.0 km./sec., and by the control of temperatures in and following the drawing process at a level to produce a boil-off shrinkage in the drawn yarn within the range of 7-20 percent, and further by control of the exposure time and temperature of the plasticizing medium in the shrinkage step to allow a shrinkage of 7-20 percent to occur without the formation of crimp to provide filaments having a crystallinity value that does not exceed 35 percent. In a preferred embodiment of the invention, the shrinkage step is carried out in a low-turbulence, heated gas stream, preferably air or steam, within a jet enclosure.

A suitable maximum machine draw ratio for the drawing step may be calculated from the expression D.R. 4.S/(1 0.0006V,) where V, is spinning speed (i.e., feed roll speed) in yards per minute.

Why the critical combination of structural characteristics outlined above for the yarn of the invention should produce unexpectedly good bulk and handle is not fully understood. Although the surprising improvement in bulk cannot be explained, it is nevertheless an observable and demonstrable fact with yarns having the critical combination of structural characteristics described above.

The above-stated structural characteristics are necessary for the development of useful fabric bulk without sacrificing utility. Thus, it is necessary that the orientation and crystallinity levels be restricted to the limits defined in order that the yarns respond properly to fabric finishing conditions. If the orientation is too high, i.e., if the measured sonic velocity values are above 3.0 kilometers per second, then the fiber bending modulus appears to be too high for the present purpose because the fibers are unable to bend within the short lengths available in the fabric. Under such conditions, improved bulk is not obtained, as is shown in the examples when a conventional, high orientation yarn is used. On the other hand, yarns of very low orientation tend to become brittle when crystallized, so that fabrics prepared from such yarns, i.e., yarns having a sonic velocity below about 1.9 kilometers per second, would be relatively useless in ordinary commercial usage. With regard to crystallinity, yarns having a crystallinity value above about 35 percent are too crystalline to develop the desired bulk by ordinary fabric finishing treatments; and yarns having a crystallinity below about 16 percent would be so amorphous as to shrink excessively upon heating, which would lead to unacceptable commercial fabrics. A unique feature of the yarns of the present invention is the presence of a low-temperature peak (below 100C.) in the tension-temperature spectrum. While the role of this feature is not fully understood, it is found in all yarns of the invention. It is possible that the reversal of tension at a relatively low temperature, as indicated by the peak, causes the individual fibers to move relative to each other and to bloom within the dimensions of a knit stitch, whereas filaments of yarns not showing this low-temperature peak appear to shrink in unison. As is known in the art, warp knit fabrics from yarns of the latter type show moderate changes in cover but no significant changes in bulk. The yarns of the invention are also characterized by the absence of crimp or twist, which contributes to better handling and knittability as well as improved fabric unifomity.

It should be noted that the yarns of the invention are low-shrinkage yarns in the sense that the normally measured boil-off shrinkage falls in the range of l to percent.

The yarns of this invention are useful in many types of fabrics, but offer an outstanding improvement in properties in warp knit fabrics. Unusually good results are obtained, as illustrated more fully in the examples, in warp knit fabrics using bar-on-bar construction when the yarns of the invention are used in combination with conventional commercial yarns. In such fabrics, best results are obtained with the yarn of this invention on the top (front) bar. In addition to bar-on-bar constructions, excellent results may also be obtained by combining the yarns of the invention with ordinary commercial yarns by twisting or by intermingling filaments to form a unitary yarn for fabric preparation.

It is emphasized that the yarns of the invention are free of significant crimp and that fabric bulk is observed only after the fabric has been constructed and heated to a temperature of about 100C. or above. Such heating takes place during normal fabric finishing procedures, as when the fabric is scoured, dyed, or heat-set on a tenter frame.

In addition to improved bulk and handle, fabrics prepared from the yarns of the invention possess excellent dyeability characteristics and show better color yield, improved color clarity and better print definition in comparison with both ordinary and set-textured polyester yarns.

DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are front and back views, respectively, of a warp-knit tricot fabric having a 2-3, 1-0 stitch on the front bar and a 1-0, 1-2 stitch on the back bar. In both figures, the front bar yarn is shown darker than the back bar yarn.

Discussion of Product Characterization and Tests The novel yarns of the present invention are composed of a synthetic linear condensation terephthalate polyester of the type described in U.S. Pat. Nos. 2,465,319 and 2,901 ,466. Preferably, the yarn is composed of a glycol terephthalate polyester which is a linear polyester in which at least about percent of the recurring structural units are glycol terephthalate units,

where G is a glycol residue. Included are copolyesters in which up to 15 percent of the terephthalate is re-' placed by a dicarboxylate of a hydrocarbon free from ethylenic unsaturation, or by a metallic salt of sulfoisophthalic acid. Typical copolyesters are formed by replacing up to about 15 mol percent of the terephthalic acid or derivative thereof with another dicarboxylic acid or ester-forming derivative thereof, such as adipic acid, dimethylsebacate, isophthalic acid, hexahydroterephthalic acid, or sodium 3 ,5- dicarbomethoxybenzene-sulfonate. Preferred glycols are ethylene glycol and hexahydro-p-xylylene glycol. Glycol terephthalate linear polyesters can readily be prepared in the oriented, relatively amorphous or noncrystalline form useful in preparing the yarns of the invention.

The yarns of this invention are composed of polymer of fiber-forming molecular weight, and have an intrinsic viscosity of at least about 0.3. Intrinsic viscosity is defined by the expression:

limit of the fraction ln m/C as C approaches 0 wherein 1;, is the viscosity of a dilute solution of the polymer in a solvent divided by the viscosity of the solvent per se measured in the same units at the same temperature; and C is the concentration in grams of the polymer per milliliters of solution. A convenient solvent for use in the measurement of intrinsic viscosity of polyethylene terephthalate is a mixture of trifluoroacetic acid and methylene chloride in a volume ratio of 1:3.

In the examples, degree of polymerization is also indicated by RV which is the relative viscosity of a polymer solution at a nominal concentration of percent. The term RV refers to the ratio of the viscosity of a 10 percent solution (2.15 grams polymer in 200 milliliters solvent) of the polymer in a solvent to the viscosity of the solvent per se measured in the same units at 25C. The solvent used for the measurement of relative viscosity in the examples is Fomal, a mixture of ten parts phenol and seven parts 2,4,6-trichlorophenol (parts by weight). A relative viscosity of 25 corresponds roughly to an intrinsic viscosity of 0.64, and a relative viscosity of 30 corresponds roughly to an intrinsic viscosity of 0.70.

The yarns of this invention are composed of filaments having a molecular orientation such that the measured values of sonic velocity fall between 1.9 and 3.0 kilometers per second, and preferably between 2.0 and 2.5 km./sec. The term sonic velocity is a polymer structural parameter related to molecular orientation along the fiber axis with higher values of sonic velocity indicating a higher degree of orientation. Sonic velocity (C) is related to the modulus of elasticity (E) by the formula E 1 1.3 C where E is in grams per denier and C is in kilometers per second. Sonic velocity relationships and test procedures are described by Charch & Moseley in the Textile Research Journal, Volume 29, page 525 (July, 1959). Briefly, sonic velocity, in kilometers per second, is measured by passing a sound wave having a frequency of about 10,000 cycles per second through the polymer structure for a known distance using apparatus known in the art. The sonic velocity values reported in the examples, unless otherwise specified, were measured with the yarns held under a tension of 0.5-0.7 grams per denier (sufficient to insure detector-specimen contact without stretching the specimen) at 72F. and 65 percent relative humidity using a dynamic modulus tester Model PPM5, manufactured by the H. M. Morgan Company, 90 Sherman Street, Cam bridge, Massachusetts.

Sonic velocity is used as a measure of orientation in preference to birefringence because birefringence is difiicult to measure with precision in the range of concern (generally greater than 0.10), and is difficult to measure for filaments of non-round cross-section. Also, because birefringence measurements are made on very short segments of a filament, an excessive number of measurements is required to give a reasonable, average birefringence value unless highly uniform filaments are under observation.

The crystallinity of the terephthalate polyester making up the filaments of the present invention can be obtained by X-ray diffraction techniques. X-ray crystallinity, as reported in the examples, is as follows: a bundle of parallel filaments of 0.020 inch (0.05 cm.) thickness is mounted with the fiber axis perpendicular to a beam of nickel-filtered Cu X-rays generated at 50 kilovolts and milliamperes and collimated through 0.020 inch (0.05 cm.) pin holes. The diffraction pattern is photographed in Ilford G X-ray film at a sampleto-form distance of 5 centimeters using an exposure time sufficient to give an optical density on the developed film of about 1.0 at the 010 diffraction maximum. The exposed film is developed for 3 minutes at 68C. in Du Pont X-Ray Developer prepared as recommended by the manufacturer. The film is rinsed 30 seconds in 3 percent acetic acid stop bath, fixed for 6 minutes in Du Pont X-Ray Fixer and l-lardener, rinsed for at least ont hour in running water and dried at room temperature. The optical density of the film is scanned along the equator using a Knorr-Alpers micorphotometer (Leeds & Northrop Model 6700 Pl, A2 assembly), set at a plate travel rate of 5 millimeters per minute and a chart speed of 2 inches per minute (5.08 cm. per minute). As is well known, the resulting curve exhibits 3 peaks, corresponding to the scattering from the 010, 110, and diffraction plates, which represent the principal scattering from glycol-terephthalate linear polyester crystallites. To estimate the crystallinity of the sample, a straight line is drawn underneath the 010 peak and tangent to the curve on either side of the 010 peak. A perpendicular line is then dropped from the highest point of the 010 peak to the 100 percent transmission axis. The height of the point of intersection between this perpendicular line and the line tangent to the curve is then designated as I representing the intensity (log. l/transmission) of the amorphous background. The height of the highest point of the 010 peak itself is designated as 1,. Crystallinity is then calculated from the following formula:

' percent crystallinity (I 1,, )/I X 100 percent The yarns of this invention are composed of filaments having an X-ray crystallinity between 16 and 35 percent measured by the above procedure.

An alternative method of measuring X-ray crystallinity which gives results in conformance with those given by the above method utilizes a Norelco X-ray diffraction unit (North American Philips Co., Inc., New York) fitted with a wide-angle diffractometer and a scintillation counter. A high-intensity copper-target tube is used at a voltage of 40 kilovolts and a beam current of 40 milliamperes. The X-ray beam is collimated with 0.5 divergence slits, 0.006 inch receiving slits and 05 scatter slits. A nickel filter is placed before the receiving slit to provide monochromatic radiation, and pulse-height discrimination is also used according to the manufacturers directions. A parallel array of fibers is mounted in the reflecting mode, and equatorial scattering is recorded at a scanning rate of 1 per minute (in 20 units) and recorded as intensity (counts per second) vs. the scattering angle, 20. The resulting curve is equivalent to the densitometer curve obtained in the first-described method (above), counts-per-second being proportional to (log. lltransmission), and the fiber crystallinity is calculated from the curve by the same procedure.

The term shrinkage tension refers to the retractive force exhibited by a yarn when heated. The shrinkage tension of terephthalate polyester filaments usually changes appreciably with the temperature to which the filaments are heated. In the temperature range 60-200 C., the yarns of the present invention show a single peak in the tension-temperature spectrum, and this peak appears at a temperature below 100c. The value of the peak shrinkage tension is less than about 0.06 gpd for the preferred yarns of the invention. Shrinkage tension is measured by mounting a looped specimen of yarn between lnvar hooks in a small oven provided with a means of heating and a means of indicating temperature. One hook is attached to a strain gauge and the other is fixed at a distance which gives a taut loop (minimum measurable tension). Heat is applied to the oven to raise the temperature at a rate of about 30C. per minute. The temperature and the tension are measured simultaneously and plotted on a graph of tension versus temperature to provide a convenient read-out of the temperature of peak tension. Measurements of this type are described by Weidner in Chemiefasern 10, 751 (1968).

The yarns of this invention are composed of continuous filaments essentially free from individual filament twist. In the case of non-round filaments, filament twist is easily observed by examination under a microscope. The methods for observing twist in round filaments involve microscopic examination of filaments illuminatee by plane-polarized light. For round filaments containing significant quantities of Ti0 filament twist may be observed by using the techniques described by Astle- Fletcher, Journal of the Textile Institute, Vol. 48, T-l 2- 8-132 (1957) and by Woods, Journal of the Textile Institute, Vol. 55, T-243-250 (1964).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples illustrate specific embodi- 2 merits of the invention. They are not intended to limit it in any manner.

EXAMPLE 1 Polyethylene terephthalate continuous filament spinning and drawing procedures using a spinning speed (feed roll speed) of 1485 ypm (1358 mpm), and single-stage drawn in a steam jet similar to that described by Pitzl in U.S. Pat. No. 3,452,132 using steam at a temperature of 160C. and a pressure of psig.

(3.4 atm.). The draw rolls, heated to the temperatures 35 shown in Table l, rotate with a peripheral speed of windup. Windup speeds are shown in Table 1. Several test yarns (coded B, C, and D) are prepared by this general process using the specific conditions listed in Table 1. Examination of the test yarns reveals that they are free of significant crimp and give no indication of individual filament twist.

For comparison, a conventional yarn (A) is melt spun in the same fashion as above but drawn in an aqueous bath of the general type described by Dusenbury in U.S. Pat. No. 3,091,805 using a temperature of 9192C. and a draw ratio of 2.4, with the draw roll heated to C. No hot relaxing jet is used.

A second conventional yarn (E) is a commercially available dull (2% TiO polyethylene terephthalate 27-filament yarn having a total denier of 40, a tenacity of 4.27 gpd, a break elongation of 27.6 percent, and a boil-off shrinkage of 8 percent. This yarn is characterized by a sonic velocity of 3.81 km./sec., an X-ray crystallinity of 28 percent, and a shrinkage-tension peak at C.

The above-described test and comparison yarns are used to knit tricot fabrics in yarn combinations shown in Table II. Greige fabric construction parameters are adjusted to give the same finished fabric construction for all samples. The fabrics are finished by subjecting them to a relaxed scour, in which they are heated from room temperature to the boil and then held 20-30 minutes at the boil, using an aqueous solution of 0.5 gmJliter of a suitable wetting agent such as Duponol RA (sodium salt of a modified alcohol sulfate) or Alkanol HCS and 0.5 gm./liter tetrasodium pyrophosphate. After rinsing, the fabric is heatset on a pin tenter for 60 seconds at C. under sufficient tension to provide 48 X 48 wales and courses per inch (19 X 19 per cm.). Properties of the finished fabrics are listed in Table II.

TATBLTEErL-P Recess CONDITIONS Draw r011 Drawn Relaxer Spin yam jet over- Windup speed Polymer temp, Draw Temp., Residence B.O.S., feed, Yarn code RV P 0. ratio 0 time, sec. percent" percent Y.P.M. (M.p.m.)

20.4 297-8 2. 37 115 0.35 (N.A.) 2,005 (2, 738) 20.0 297-8 2. 02 00 0. 43 18.6 15.0 2,500 (2, 35s) 20.7 295-6 2.02 98.5 0.43 17.5 0.5 2, 740 2, 505) D 20.0 297-8 2.02 112 0. 43 7.8 3.1 2,010 (2, 001) E (A commercial P.E.T. yarn).

Percent shrinkage in boiling water.

3000 ypm (2743 mpm) to impart a draw ratio of 2.02. T LE Ib.-YARN PROPERTIES Moving from the draw rolls, the yarn passes through a 50 shflnkago second (relaxing) et having a design similar to that M1510" Peak on 0 shown in FIGS. 1 and 2 of U.S. Pat. No. 3,261,071 to 511,050. 5, Clendening where the yarn is treated at reduced tension with air supplied at a temperature of 220C. and a pressure of 55 psig. Tension in this second jet is mainv11 tained at a very low level by passing the yarn leaving the et over snubbmg pins before forwarding It to a TABLE II Fuhrlc N11 I17 141-1 48 39 50 10 Yarn:

Front. (top) bar A A B C 1) X Back (bottom) bur A E A A A Xz Stitch:

1050100: 2-3, 1 2-3, 1.0 2-3, 1-0 2-3, 111 2-3, H) 2-3, 1-0 2-3, H) Back bar ..1-0, 1 1-0, 1-2 1-0, 1--2 1 -0, 12 10, 1-2 10, 12 1-0, 1 2 Runners (111.):

Front bur 04. 4 02. 7 02 111. 0 03. 7 01. 0 05. a Buck1 ur '17 45.8 44 411.6 411.5 411.5 4% 11111.10, front/buck 1.37/1 1.37/1 1.4111 1.33/1 1 10/1 1 33/1 1.37/1 Fabric inches per ruck r H X K )1 N m linislmrl count, (w.p.i. x 1:.y1.i.) M1 )1 62 48 x 48 47.6 :1 1'10 413 x 4% N1 1143 45 x (M 11' x fiil 'lAli m: 11 Continued Fabric N lli '17 1 11 l 15 3!) 5U 11) Weight:

Oz./sr yd 2. 7 2.8 2. 7 2. 6 2. 7 2.8 2. 8 (Ems/sq. m 1 (92) (95) (92) (88) (92) (95) (95 Bulk (co/gm):

At 3 gin/0m. loading... 3. 3 3. 6 3. 58 5. 8 5.0 4. 8 3. 8 At 40 grim/cm. loading 3. 0 3. 2 3.14 4. 6 4. l 4. 1 3. 3 At 239 grrL/cm. louding 2. 7 2. 8 2. 81 3. 4 3. 2 3. l 2. 8

4459;, nos. b 14% BOS.

A further comparison illustrating the improvement over mixed shrinkage knits of the type described by Kasey in U.S. Pat. No. 3,041,861, is provided by fabric 10. Fabric 10 is knit with a 4-6 percent boil-olfshrinkage yarn on the front bar and a 14 percent boiltemperature of 92C., where drawing occurs, and then on to draw rolls moving at a surface speed of 2998 ypm (2740 mpm). Other process details are shown in Table III. The 40-denier/27-filament yarn is coded control yarn 2.

off-shrinkage yarn on the back bar. Preparation of 15 The yarns produced as described above are examined these yarns, X, and X is described subsequently (Exand found to have the structural features listed in the ample VI). The measured bulk of fabric 10, as shown Table. in Table II, is not significantly greater than that of fab- Jersey tricot fabrics are knitted using the aboverics 46, 47 and 14ll which are knit from yarns having described test yarn 1 and conventional yarn 2 as little or no shrinkage differential. 7 specified in Table IV. These fabrics are finished by sub- Fabric bulk is obtained by measuring the fabric thickjecting them to a relaxed scour, in which they are ness and dividing this thickness (in cm.) by the area heated from room temperature to the boil and then density (gm/cm?) to obtain bulk in cmflgm. The held 30 minutes at the boil, using an aqueous solution thickness is measured under loadings of 3, 40, and 239 of 0.5 gm./liter of a suitable wetting agent such as gmJcrn. to obtain bulk properties corresponding to a Duponol D (sodium lauryl sulfonate) and 0.5 gm./liter range of tactile environments. tetrasodium pyrophosphate. After rinsing and drying,

Inspection of the data in Table II clearly reveals that the fabric in TAI3LE Ill Shrinkage tension, Percent Draw roll maximum yarn Spin Windup Over- X-ray C.)/ boil-oil Yarn Polymer temp. Temp. Time Draw feed, l)en./ SV(km./ cryst. tension shrinkcode RV 0.) 0.) (see) ratio (Y.p.m.) (M.p.m.) percent fil. sec.) percent) (g.p.d.) age 1 20.5 293 100 0. 43 2.02 2, 767 2, 529 8.6 /14 2.24 30 00/0035 5.4 2 30 307 110 0. s5 3. 72 2,958 (2, 703) 1.3 27 3.03 as 144 0. 274 8.0

the tricot fabrics prepared with the test yarns of this in- TABLE IV vention, in combination with conventional yarns, ex- Yarn (Table III): hibit a significant imprpvemem in bulk- In addition, I 52213133.::::::::::::::::::::::::::::::::::I: i i ammatlon of the fabrics reveals that the fabrics pre- 40 l g bar q H, H] H H) pared from the test yarns of the invention possess an Back bar 1-0,1-2 1-0,1-2 attractive spun-like handle without the objectionable g-$332 51 62 62 slickness of conventional synthetic fabrics, Back bar 44 44 Ratio (front back) 1. 41 41 EXAMPLE n 45 48-52 50-52 Weight (o7../yd 2. 7 2- 7 This example illustrates the preparation of a yarn of B ik (cc,/gm,); this invention from a basic dyeable copolymer of P Y- it io gi'il iii i iiiiigjlljiIIIIIIIIIIIII 313 313 ethylene terephthalate. At 230 gm./cm. loading s. 4 a. 0

A copolymer of polyethylene terephthalate containing 2 mol. percent S-(sodiumsulfo)-isophthalate in the 50 molecule and having a relative viscosity of 20.5 is melt is heat-Set a P Enter for Seconds at spun into a l4-filament yarn in which all filaments have under sufficient tension to provide the wale and course a trilobal cross-section. Following the general procounts specified in Table IV. cedure of Example I, the undrawn yam pas ove a Inspection of the data in Table IV clearly indicatts feed roll moving with a surface speed of 1483 ypm 55 that the test yarn of this invention imparts a significant (1356 mpm). through a steam draw-jet and then improvement in bulk and further, subjective evaluation over draw rolls rotating at a surface speed of 3001 reveals that the tricot fabric of test yarn possesses a disypm (2744 mpm). Other specific process details tinct spun-like handle in contrast to the slick filamentare summarized in Table III. From the draw roll, like character of the conventional synthetic filament the yarn is passed through a relaxing jet supplied 0 yam fabrics. with air at 55 psig. (3.7 atm.) and heated to a temperature of 250C., from which it proceeds to a windup EXAMPLE operating at 2767 ypm (2529 mpm). This is designated This example illustrates the preparation of yarns of test yarn l in Table III. the present invention from copolymers prepared from A companion conventionaPyam is prepared by terephthalic acid and an aliphatic dicarboxylic acid.

spinning 30 RV polyethylene terephthalate homopolymer at a spinning speed of 806 ypm (737 mpm). The yarn passes through an aqueous bath maintained at a A copolymer of ethylene glycol, terephthalatic acid and sebacic acid in which the sebacic acid residues comprise 10 mol. percent of the acid units in the polymer, and which has a relative viscosity of 30.1, is melt spun at 298C. to give a 27-filament yarn in which the filaments have a trilobal cross-section. This yarn is drawn in a steam jet, as described in Example 1, which is supplied with steam at a temperature 160C. and a pressure of 50 psig (3.4 atm.), and then passed over draw rolls operating at a surface speed of 3000 ypm (2743 mpm). The drawn yarn passes through a relaxing jet supplied with air at 55 psig. (3.7 atm.) which is heated to a temperature of 404C. and then to a windup operating at 2950 ypm (2697 mpm). The yarn is designated test yarn 3, Table V.

For comparison, a control yarn (4) is prepared as above, with the draw yarn bypassing the relaxing jet and proceeding directly to the windup. Process details are shown in the table.

Jersey tricot fabrics are knit utilizing the test copolymer yarns (3) and control copolymer yarns (4) in the front bar with the conventional 40-27 yarn described in Table 111 as a common back bar yarn as specified in Table VI. These fabrics are scoured for 30 minutes at the boil in an aqueous solution of 0.5 gmJliter Duponol D and 0.5 gm./liter tetrasodium pyrophosphate, rinsed, centrifuged and dried. The dried fabric is heat-set on a pin tenter frame for 60 seconds at 190C. to the Wale and course counts given in Table VI. Fabric bulk data measured under the three compressive loadings of 3, 40, and 239 gmJcm. clearly show the bulk improvement imparted by the copolymer test yarns of the invention relative to that imparted by the appropriate control yarns. A soft spun-like handle is also readily apparent for the test yam items in contrast to the slick filament-like handle of the control tricots.

that used in Example 1) which is supplied with steam at a temperature of 160C. and a pressure of 50 psig. (3.4 atm.). The yarn proceeds from the jet to and around draw rolls heated to 101C. and operating at a peripheral speed of 3005 ypm. (2747 mpm). The draw ratio is 2.09 X, and the residence time on the hot draw roll is 0.43 second. The drawn 38 denier yarn is wound up at 3010 ypm. (2752 mpm). A skein of this yarn is then allowed to relax for 10 minutes in water at a temperature of 66C. A shrinkage of 5.0 percent is noted. After drying, the shrinkage tension of the yarn as a function of temperature is measured and the yarn is found to have a shrinkage tension peak at 95C., and maximum shrinkage tension of 0.027 gpd. X-ray measurements indicate 23 percent crystallinity and sonic velocity measurements give a value of 2.52 kilometers/sec. measured under a tension of 0.7 grams per denier. The yarn is substantially free of crimp, and examination under a microscope between crossed polarizers gives no indication of individual filament twist.

Jersey tricot fabric is knitted using the above described yarn, designated test yarn 7, as a front bar yarn in combination with a back bar of conventional yarn 2 (Table 111). This tricot fabric is finished according to the procedure specified in Example 111 and compared to a control tritot fabric (cf., Table IV) having front and back bar yarns of the conventional yarn 2 which is similarly finished. Fabric data given in Table V11 shows that the tricot fabric containing yarn of this invention has appreciably greater bulk. Upon subjective evaluation of the fabrics, the preferred spun-like handle of the test yarn tricot is clearly evident.

TABLE V Shrinkage Draw Rolaxer jet air ten. peak Spin speed rnll Windup SV, X-ray Shrink- Yarn Draw temp. Temp. km.l cryst., Tension age, Description code Y.p.rn. (M.p.m.) ratio C.) C.) P.s.i. Y. p.m. (M.p.m.) Den. sec. percent C. (g.p.(l.) percent 2G-T/l0 ((901,110) 3 l, 433 (l, 310) 2. 0 04 404 55 2, 950 (2, 696) 68. 0 l. 93 32 64 0. 031 0. 2 2 1.0

TABLE VI 7 TABLE vn Yarns:

Front bar (Table v s 4 Yams Back bar (Table III) 2 2 Fr nt Bar 7 2 titch: Back Bar (Table 111) 2 2 Front bar 2-3, 1-0 2-3, l-O S i h R g g 1 Front Bar 24, l() 24, l-() l forit 152.. 65 64 Back Back barn u: 44 4:; Rune Ratio (mm back).-- 1.41 1. 49 Front Bar 62 62 Fabric in. per rack... s 3 Back Bar 44 44 Finished count (w.p.l 48-50 47-69 Ratio (Front/Back) 1.41 1.41 gg fi z ggf) 1 0 Fabric in. per rack 8 8 At a mJm'nn loading 4.4 3.0 i 7 53 5044 At 40 gnu/cm. loading 3. 8 2. 0 l cpl 7 At 239 gm./cm. loading 8.2 2.6 t (OZJYd- Bulk (cc./gm.)

at 3 gmjcm. loading 5.9 3.6 at 40 gmJcm. loading 4.7 3.2 EXAMPLE [v at 239 gmJcm. loading 3.7 3.0 This example illustrates an alternative method of pre- EXAMPLE V Parmg a pdyester yam of the Present mvemlon' Po1y(cyclohexane-1,4-dimethylene terephthalate) Polyethylene terephthalate having a relative viscosity of 30.2 and containing 2 weight percent TiO, is melt spun at 294C. into a yarn composed of 14 trilobal cross-section filaments. The quenched filaments are passed around a feed roll moving at 1434 ypm. (1311 mpm) and then through a steam draw jet (similar to draw bath to and around unheated draw rolls operating at a peripheral speed of 2750 ypm (2514 mpm) and is wound up at 2666 ypm (2437 mpm). The yam has a boil-off shrinkage of 40.6 percent.

A skein prepared from this yarn is relaxed 10 minutes in 80C. water during which time it shrinks 11.4 percent. The skein is dried and backwound. The 71-denier yarn has a crystallinity of 18 percent, a sonic velocity of 2.24 km./sec., a peak shrinkage tension of 0.035 gpd at 80C. and exhibits a boil-off shrinkage of 5.6 percent. The yarn is designated test yarn 8.

A tricot fabric is prepared with the above-described yarn as a front bar yarn in combination with the conventional yarn 2 (Table III) in the back bar. The fabric is relax scoured, dried, and heat-set as described in Example III. Fabric properties are given in Table VIII. The test yarn is found to impart an appreciable amount of bulk, as well as improved tactile aesthetics, to the tricot fabric.

Measurement of the X-ray crystallinity of fibers of poly(cyclohexane1,4-dimethylene terephthalate) requires a modification of the previously described procedures because the polymer contains a mixture of cisand transisomers of the glycol with the two crystal dimensions being slightly different. In the modified procedure, found suitable for crystallinities in the range 16-35 percent, the intensity vs. scattering angle (20) curve is prepared as usual, points on the curve located at 20 valus of 18.5 and 26.7", and a line drawn between these two points. A vertical line is drawn from the baseline to the intensity curve at a 26 value of 22.3 (the approximate location of the 100 diffraction). This vertical line intersects the intensity curve at point I, and the first-drawn line at point 1,. Percent crystallinity is calculated from the expression:

Percent crystallinity (I I,,)/I, X 100.

TABLE VIII Yarn Code Front Bar 8 Back Bar (Table III) 2 Stitch Front Bar 2-3, l-

Back Bar 1-0, 1-2 Runners(in.)

Front Bar 64 Back Bar 44 Ratio (Front/Back) 1.45 Fabric in. per rack 8 Finished Count (wales/in.-courses/in.) 40-55 Weight (On/Yd?) 3.53 Bulk (cc/gm.)

at 3 gmJcm. loading 4.3

at 40 grnJcm. loadinG 3.6

at 239 gmJcm. loading 3.0

EXAMPLE V] For comparison with the excellent improvement in bulk shown by the yarns of this invention'in Example I, a typical prior art fabric, as illustrated by Kasey in US. Pat. No. 3,041,861, is prepared from conventional polyester yarns. In accordance with the teachings of the patent, a warp knit bar-on-bar fabric is prepared from two yarns possessing a large difference in shrinkability. This fabric is then compared directly with a fabric knit from a single yarn (i.e., all the same shrinkage) under similar conditions. The yarns are prepared as follows: polyethylene terephthalate having an RV of 30 and containing 2.0 weight percent TiO is spun at about 308C. through a spinneret having 54 Y-shaped orifices. The trilobal filaments are quenched with a crossflow stream of air at 125 cfm and 70F, then passed around a feed-roll assembly (four wraps) maintained at 933 ypm (852 mPm), through an aqueous finish bath at 92C. and onto a set of draw rolls (13 A wraps) running at a surface speed of 2998 ypm (2741 mpm), and then to a dual windup at 2900 ypm (2862 mpm) to maintain a threadline tension of 15 grams. The draw ratio is 3.2:] and the draw rolls are held at 140C. Two ends of 40-denier 27-filament yarn, coded x1, are obtained having representative properties of 4.0 gpd tenacity, 24 percent break elongation, 1 29 gpd initial modulus and a boil-off shrinkage (BOS) of 4-6 percent. Representative samples of these yarns have an SV of 3.22, an X-ray crystallinity of 45 percent and a shrinkage tension peak at 180C.

A high shrinkage 40-27 polyethylene terephthalate yarn is prepared using the above procedure with the exception that the draw rolls are maintained at a temperat0re of 94C. Representative properties of this yarn, coded X2, are 3.7 gpd tenacity, 30 percent break elongation, 145 gpd initial modulus, a boil-off shrinkage of about 14 percent, an SV of 3.92 km./sec., an

X-ray crystallinity of 16 percent, and a shrinkage tension peak at 134 C.

The normal shrinkage 40-27 polyethylene terephthalate yarn described in Example I as yarn A is used in both bars to make a tricot control fabric (Fabric No. 47, Table II).

In this comparison experiment, the yarns are prepared for knitting by backwinding onto cones and then transferring the yarns to 7 inch 18 cm.) section beams for knitting on a 28 gauge tricot machine. Knitting and fabric details are summarized in Table IX. The knitting conditions of the fabric containing the low-shrinkagelhigh-shrinkage yarn combination are adjusted to give a greige fabric which achieves the desired fabric weight under low tension finishing conditions. Finishing conditions, i.e., relaxed scour followed by heat setting at dry width, are such that maximum available bulk can be developed. It is found that under these optimum conditions only a marginal improvement in fabric bulk is obtained with the mixed-shrinkage fabric over the second fabric prepared from yarns having no difference in shrinkage.

TABLE 1X Comparison Fabrics Fabric Mixed Shrinkage Normal Yarn Front (top) bar X1 X3 Back (bottom) bar X2 X3 Stitch Front bar 2-3, l-O 2-3, I()

Back bar I-(), 1-2 l-0, l-2 Runners Front bar 65.75 in. 62.7 in.

Back bar 48 in. 45.8 in. Ratio l.37/l l.37/l Fabric in. per rack 10 in. 8 in. Finished count 43 X 54 48 X 48 (wpi X cpi) Fabric wt. (oz./yd.') 2.7 2.8 Bulk (cc/gm.)

at 3 gmJcm. loading 3.9 3.6

at 40 gmJcm.

loading 3.3 3.2

at 239 gmJcm.

loading 2.9 2.8

The comparison experiment described above demonstrates that appreciable improvement in bulk is not obtained when two conventional prior art yarns with boiloff shrinkages differing by as much as percent are combined in one tricot fabric. In contrast, as illustrated in the previous examples, the yarns of the present invention used in combinations with ordinary commercial polyester yarns provide a marked improvement in bulk as well as an improvement in tactile aesthetics. Furthermore, since the yarns of the invention are free of significant crimp, they offer outstanding processibility in knitting operations whereas prebulked yarns are difficult to knit. Although the advantages of the yarns of the invention are realized primarily in warp knit fabrics, such as tricot, it is appreciated that the yarns are also useful in preparing weft knits such as fullfashioned and circular knits and also woven fabrics such as taffeta, twill, oxford, satin, and basket Weaves. Warp knit fabrics are particularly useful in mens shirts, womens dresswear, uniforms, blouses and intimate apparel.

EXAMPLE VII Polyethylene terephthalate containing 2 weight percent TiO is melt spun to give a 14-filament strand in which all filaments have a trilobal cross section. The quenched strand is passed over a feed roll operating at a surface speed of 1271 yards per minute (1162 meters per minute), then through a jet enclosure supplied With steam at a temperature of 190C. at a pressure of 50 psig. (3.4 atm.), and then around draw rolls operating at a surface speed of 3060 ypm (2798 mpm). The draw ratio is 2.4: l The draw rolls are enclosed in a box heated with circulating air maintained at a temperature of 92-93C. The drawn yarn proceeding from the enclosed draw rolls passes through a relaxing" (shrinkage) jet enclosure supplied with air at a pressure of 55 psig (3.7 atm.) and a temperature of 290C, then around a change-of-direction roll to a driven letdown roll assembly running at a surface speed of 2600 ypm (2377 mprn), and then to a windup operating at 2643 ypm (2417 mpm). The percent overfeed to the relaxing jet, based on letdown roll speed, is 17.3 percent. The percent net overfeed, based on windup speed, is 15.5 percent.

A sample of drawn yarn prepared by going directly from the draw rolls to windup, by-passing the relaxer jet and letdown roll, has the properties listed in Table X.

TABLE X DRAWN YARN PROPERTIES Denier 35.7 Tenacity (gpd) 3.05 Elongation (36) 73.1 Modulus (gpd) 100.2 Boil-off Shrinkage 17.2 Sonic Velocity (Km/sec.) 2.68

The relaxed yarn which is wound up in the abovedescribed process has the properties listed in Table XI.

TABLE XI RELAXED YARN PROPERTIES Denier 42.8 Tenacity (gpd) 2.44 Elongation (96) 100.8 Modulus (gpd) 50.2 Boil-off Shrlnkage (76) 4.9 Sonic Velocity (Km.lsec.) 2.17 Shrinkage Tension Peak (C.) 82 Maximum Shrinkage Tension (gpd) 0.026 X-Ray Crystallinlty (96) 25 Using single-end warping facilities, test yarn (VIIl prepared by the process described above is knit into a tricot fabric as the front-bar yarn along with a commercial polyester yarn (T-57) similar to Yarn E in Table lb in the back bar. The greige knit fabric is given a finishing treatment similar to that described for knit fabric in Example I. Fabric construction parameters and finished fabric properties are summarized in Table XII along with similar parameters and properties for a comparison fabric knit with the conventional yarn in both the front bar and back bar. The improved bulk and spunlike handle of the test fabric are readily apparent.

TABLE XII TRICOT FABRIC PROPERTIES YARNS Front Bar Test VII-l T-57 Back Bar T-57 T-57 STITCH Front Bar 2-3, 1-0 2-3, 1-0

Back Bar 1-0, l-2 1-0, 1-2 RUNNERS (|NS.)

Front Bar 62 62 Back Bar 44 44 Ratio Front/Back 1.41 1.41 Fabric in. per rack 8" 8" Weight (oz/yd?) 2.87 2.80 Finished count (wpi X cpi) 41 X 63 41 X 65 BULK (cc! At 3 gm. cm. loading 4.77 3.35

At 40 gmJcm. loading 3.82 3.02

At 239 gmJcrn. loading 3.12 2.77

EXAMPLE VIII Following the general procedure of Example I, polyethylene terephthalate containing 2 weight percent of TiO, is melt-spun through a 14-hole spinneret to give a yarn in which all filaments have a trilobal cross section. The quenched, undrawn yarn passes over a feed roll rotating with a surface speed of 960 ypm (878 mpm), through a jet enclosure supplied with steam at a temperature of C. and a pressure of 50 psig (3.4 atm.), and then over draw rolls operating at a surface seed of 3010 ypm (2752) mpm). The draw ratio is 3.14:1. The draw rolls are enclosed in a box heated with circulating air at a temperature of 78C. which gives a drawn yarn with a boil-off shrinkage of 17 percent. As the drawn yarn proceeds from the draw rolls, it passes through a relaxing jet enclosure supplied with air at 55 psig. (3.7 atm.) and a temperature of 268C, and is then passed around an idler roll to a driven letdown roll assembly rotating at a surface speed of 2593 ypm (2371 mpm). The relaxed yarn then proceeds to a windup rotating at a surface speed of 2631 ypm (2406 mpm). Threadline tension measurements made on the yarn immediately before it enters the relaxing jet give a value of 6.0 grams, and immediately following the relaxing jet, but before the letdown rolls, give a value of 0.2 grams. The tension on the yarn measured at a point immediately above the windup is 12 grams. A calculation of the percent overfeed to the relaxing jet gives a value of 16.2 percent overfeed based on letdown roll speed, and a value of 14.5 percent overfeed based on windup speed. The properties of the relaxed yarn are summarized in Table XIII.

TABLE XIII PROPERTIES OF RELAXED YARN Denier 41.0 Tenacity (sp 2.97 Elong. (36) 51.9 Modulus (gpd) 68.0

Boil-off Shrinkage 3.9 Shrinkage Tension Peak (C.) 98 Maximum Shrinkage Tension (gpd) 0.057 Sonic Velocity (kL/sec.) 2.64 Crystallinity (96) 31 A single end of test yarn prepared by the above process is knitted into a tricot fabric using the test yarn on the front bar and a commercial (T57) 40-denier 27- filament polyethylene terephthalate yarn on the back bar. The knitted greige fabric is then finished in a manner similar to that discussed in Example I. Measured properties are summarized in Table XIV. The Table also includes properties of a comparison fabric knitted with the T57 yarn on both front and back bars. The improvement in bulk provided by the test fabric is evident from the data in the Table.

TABLE XIV FABRIC PROPERTIES Fabric Test VIII Comparison Yarn Front Bar Test T-57 Back Bar T-57 T-57 Finished Count (wpi X cpi) 46 X 60 52 X 56 Weight (oz/yd!) 3.13 3.14 Bulk (cc/gm) at 3 gmJcm. loading 3.89 2.47

at 40 gin/cm. loading 3.24 2.24

at 239 gmJcm. loading 2.76 1.98

100C. which is the only peak found between 60 and 2. A yarn as defined in claim 1 wherein said sonic velocity value is between 2.0 and 2.5 kilometers per sec- 0nd.

3. A yarn as defined in claim 1 wherein said tension peak is at a temperature between C. and C.

4. A yarn as defined in claim 1 wherein the peak tension at said peak is less than about 0.06 grams per denier.

5. A yarn as defined in claim 1 composed of ethylene terephthalate polyester. 

2. A yarn as defined in claim 1 wherein said sonic velocity value is between 2.0 and 2.5 kilometers per second.
 3. A yarn as defined in claim 1 wherein said tension peak is at a temperature between 80*C. and 100*C.
 4. A yarn as defined in claim 1 wherein the peak tension at said peak is less than about 0.06 grams per denier.
 5. A yarn as defined in claim 1 composed of ethylene terephthalate polyester. 